A Magento module to use Postmark instead of Core e-mail module.
Forked from a module by Sumo Heavy that has since been taken offline.
This module overwrites the Magento e-mail model so that outgoing mail is passed through Postmark.
Accessible via Stores > Configuration > Services > Postmark Integration
Enable it to start using Postmark instead of core e-mail model
Your own Postmark API key
There is a test suite created for the initial module, but it is not currently maintained and will almost certainly not pass.
It is left in place with the goal of updating it to work correctly again in the future.